Method and arrangement for pilot pattern based control signaling in mimo systems

ABSTRACT

A radio base station, user equipment (UE), and method of control signaling in wireless communication systems. Control information is transferred from a base station to at least one UE, via a plurality of common pilot channels. A set of unique pilot sequences is predefined, and the base station assigns specific pilot sequences from the set of pilot sequences to specific common pilot channels, forming a pilot sequence assignment pattern representing specific control information. The UE, having knowledge of the relations between pilot sequence assignment patterns and control information, interprets the received pilot sequence assignment pattern as specific control information. The method is particularly well suited for broadcast type control information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/549,304 filed on Nov. 20, 2014, which is a continuation ofU.S. patent application Ser. No. 12/514,762 filed on May 13, 2009, nowU.S. Pat. No. 8,923,423, which is a 371 of International Application No.PCT/SE2006/050469, filed Nov. 13, 2006, the disclosures of which arefully incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method and arrangement of providingcontrol signaling. In particular, the present invention relates tocontrol signaling in MIMO based communication systems.

BACKGROUND

The demand for traffic capacity, coverage and reliability in thewireless communication systems is seemingly ever-increasing. Onebottleneck in the traffic capacity is the limited frequency spectrumavailable for communication purposes, the limitation being bothphysical—only part of the frequency spectrum is suitable forcommunication and the information content per frequency and time islimited, and organizational—the useful part of the spectrum is to beused for a number of purposes including: TV and radio broadcast,non-public communication such as aircraft communication and militarycommunication, and the established systems for public wirelesscommunication such as GSM, third-generation networks (3G), WirelessLocal Area Networks (WLAN) etc. Recent development in the area of radiotransmission techniques for wireless communication systems showpromising results in that the traffic capacity can be dramaticallyincreased as well as offering an increased flexibility with regards tosimultaneously handling different and fluctuating capacity needs.Promising techniques are based on the concept ofMultiple-Input-Multiple-Output (MIMO) see for example A. Goldsmith etal. “Capacity Limits of MIMO Channels”, IEEE Journal on Selected Areasof Comm., VOL. 21, NO. 5, JUNE 2003. Compared to presently usedtransmission techniques such as TDMA (as used in GSM) and WCDMA (as usedin UMTS), the above exemplified technique represents a much better usageof the available radio frequency spectrum. As an example of thecapabilities of, but also the requirement set forth by, the newtransmission techniques, the MIMO wireless systems will be brieflydescribed with references to FIG. 1 (prior art). A comprehensivedescription of the basic principles as well as recent development andareas of research of MIMO is to be found in the above referred articleby A. Goldsmith et al.

A radio link in a MIMO system is characterized by that the transmittingend as well as the receiving end may be equipped with multiple antennaelements. The idea behind MIMO is that the signals on the transmit (TX)antennas at one end and the receive (RX) antennas at the other end are“combined” in such a way that the quality (bit-error rate, BER) or thedata rate (bits/sec) of the communication for each MIMO user will beimproved. Such an advantage can be used to increase both the network'squality of service and the operator's revenues significantly. A coreidea in MIMO systems is space-time signal processing in which time (thenatural dimension of digital communication data) is complemented withthe spatial dimension inherent in the use of multiple spatiallydistributed antennas. A key feature of MIMO systems is the ability toturn multipath propagation, traditionally regarded as a limiting factorin wireless transmission, into a benefit for the user. MIMO effectivelytakes advantage of random fading and when available, multipath delayspread, for increasing transfer rates. The prospect of significantimprovements in wireless communication performance at no cost of extraspectrum (only hardware and complexity are added) has naturallyattracted widespread attention. MIMO is, due to the promisingpossibilities, considered for enhancing data rates in third generationcellular systems, specifically for the High-Speed Downlink SharedChannel (HS-DSCH).

The multiplexing alone is, as previously mentioned, not enough forachieving the dramatic increase in gain. Advanced coding/decoding andmapping schemes, e.g. the space-time coding, is essential. A knowledgeof the radio channel is needed for the decoding already in today'sexisting wireless systems such as GSM and UMTS, and in the multi-antennasystems this knowledge is absolutely critical. In some of the mostpromising implementation proposals for MIMO, the knowledge of thechannel, is used not only in the demodulation performed in the receiverside, but also in the encoding and modulation on the transmitting sidewhen the system employs adaptive rate control. With adaptive ratecontrol, the transmitter determines a transmission rate appropriate fora given radio channel condition. When the channel condition is good, ahigh transmission rate is used, whereas when the channel condition isbad, a low transmission rate is used. The transmission rate determinesthe modulation order (e.g., QPSK versus 16QAM) and the coding rate offorward error-correction code (FEC) on the transmitting side. Accuraterate control is highly desirable in that it improves system and userthroughput. In WCDMA release 5, transmission rate control is facilitatedby a channel quality indicator (CQI) feedback provided by a mobileterminal or user equipment. The CQI indicates the receiversignal-to-interference-plus-ratio (SINR) under the current radiocondition. In essence, a CQI indicates the highest transmission datarate in order to achieve a certain block error rate (e.g., 10%) undercurrent radio condition. The use of CQI according to WCDMA release 5 isdescribed in 3rd Generation Partnership Project (3GPP), TechnicalSpecification Group Radio Access Networks: Physical channels and mappingof transport channels onto physical channels (FDD), 3GPP TR 25.211,version 5.5.0, September 2003, and in 3rd Generation Partnership Project(3GPP), Technical Specification Group Radio Access Networks: PhysicalLayer Procedures (FDD) 3GPP TR 25.214, version 5.9.0, June 2003.

Auxiliary control signaling may be needed to facilitate accurate CQIestimation and rate control in a MIMO system. For example, instantaneouspower and code allocation may be signaled from the base station tomobile terminals to facilitate CQI estimation. Since this type ofinformation is signaled to all the mobile terminals in the system, thismay be considered as a broadcast control information. Other broadcastcontrol information may also be needed to facilitate accurate CQIestimation.

In UMTS a common pilot channel (CPICH) is used for the characterizationof the dedicated radio channel First, the receiver relies on the CPICHto obtain an estimate of the channel impulse response that is neededduring demodulation. With adaptive rate control, the receiver may alsouse the CPICH to estimate the highest transmission rate that the currentchannel condition may support in order to satisfy a targeted block errorrate requirement. This transmission rate is then communicated back tothe transmitter in a form of channel quality indicator (CQI) per WCDMArelease 5. The CPICH is a code channel carrying known modulated symbolsscrambled with a cell-specific primary scrambling code. UMTS alsoprovides for secondary CPICHs, which may have individual scramblingcodes, which typically are used in operations of narrow antenna beamsintended for service provision at places with high traffic density. Asimilar approach is suggested for MIMO based systems. In MIMO aplurality of common pilot channels (CPICHs), corresponding to the numberof transmitting antennas or antenna streams, are used to characterizeeach of the channels between a transmit antenna and a receive antenna.The requirement for accurate channel characterization in combinationwith the plurality of CPICHs can make the control signaling relativelyextensive, and will take up valuable transmission resources.

Recently, a promising new MIMO technique called PARC(Per-Antenna-Rate-Control) [1] has been proposed for use with HS-DSCH,see S. T. Chung et. Al, “Approaching eigenmode BLAST channel capacityusing V-BLAST with rate and power feedback”, Proc. IEEE VTC′01-Fall,Atlantic City, N.J., October 2001. The scheme is based on a combinedtransmit/receive architecture that performs independent coding of theantenna streams at different rates, followed by the application ofsuccessive interference cancellation (SIC) and decoding at the receiver.It requires feedback of the per-antenna rates which are based on thesignal-to-interference-plus-noise ratios (SINRs) at each stage of theSIC. With this scheme, it has been shown that the full open-loopcapacity of the MIMO flat-fading channel may be achieved, thus offeringthe potential for very high data rates.

The anticipated advantages of novel transmission techniques such asMIMO, PARC-MIMO and cooperative relaying is well demonstrated in theart. However, to fully take advantage of the increased data rates, thecontrol signaling must not be allowed to become too extensive.

SUMMARY

To fully take advantage of the potentially high data rates offered bynovel transmission techniques such as MIMO and PARC-MIMO, therequirement for feedback is high. At the same time, the amount ofcontrol signaling must be kept at a reasonable level. Therefore,improved control signaling procedures are needed.

The object of the present invention is to provide a method andarrangements that overcome the drawbacks of the prior art techniques.

In the method according to the invention, control information istransferred from a first radio node to at least one second radio nodevia a plurality of common pilot channels. A set of unique pilotsequences has been pre-defined, and the first radio node assignsspecific pilot sequences from the set of pilot sequences to specificcommon pilot channels, forming a pilot sequence assignment patternrepresenting specific control information. The second radio node, havingknowledge of the relations between pilot sequence assignment patternsand control information, interprets the received pilot sequenceassignment pattern as the specific control information. The method isparticularly well-suited for broadcast-type control information, and thefirst radio node is typically a radio base station, and the second radionode is typically a user equipment.

Preferably the method comprises the steps of:

-   -   the radio base station recognizing a need for updating of        broadcast-type control information;    -   the radio base station selecting a pilot sequence assignment        pattern, based on a pre-determined relation between sequence        assignment patterns and control signaling information, and        transmitting pilot sequences on the common pilot channels        according to the selected pilot sequence assignment pattern;    -   the user equipment receiving the pilot sequences and determining        pilot sequence assignment pattern by detecting the selection of        pilot sequence transmitted by the radio base station;    -   the user equipment extracting the control signaling by using the        pre-determined relation between sequence assignment patterns and        control signaling information.

The individual pilot sequences as well as the relations between pilotsequence assignment patterns and the control information is preferablyshared between all relevant nodes or entities, in the communicationsystem. Even more preferably the relations are standardized.

The method could advantageously be used to broadcast information aboutthe current power and/or code allocation of the base station to the userequipment. Another type of control information suitable to bebroadcasted in this manner relates to network controlled feedback. In anetwork control feedback scenario, a feedback threshold parameter can bebroadcasted from the base station to indicate to each user equipment theconditions under which the user equipment is allowed to feed backdifferent amount or type of information.

One advantage afforded by the present invention is the possibility totransfer control information without taking up valuable radio resources.

A further advantage is that the detections of individual pilot sequencescan be made with conventional methods and means and are not excessivelycomplex or capacity consuming.

Yet a further advantage is that the method according to the invention iswell suited for broadcasting code and power allocations associated withthe promising PARC-MIMO technologies. The method according to theinvention may also be applied to other access technologies such asOrthogonal Frequency Division Multiplexing (OFDM) as discussed inconnection with the long term evolution of UMTS and 4G.

Embodiments of the invention are defined in the dependent claims. Otherobjects, advantages and novel features of the invention will becomeapparent from the following detailed description of the invention whenconsidered in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to thedrawing figures, wherein

FIG. 1 is a schematic illustration of a wireless communication systemwherein the methods and arrangement according to the present inventionmay be implemented;

FIG. 2 illustrates schematic illustrations of the principles ofconveying control information according to the present invention;

FIG. 3 is a flowchart illustrating a first embodiment of the methodaccording to the present invention;

FIGS. 4a-4b schematically illustrate pilot sequences, (a) un-shortenedand (b) shortened, suitable for an embodiment of the invention;

FIGS. 5a-5b schematically illustrate a radio base station and userequipment according to the present invention; and

FIG. 6 is a flow chart illustrating a second embodiment of the methodaccording to the present invention.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements.

A possible communication scenario wherein the method and arrangementaccording to the present invention is schematically illustrated inFIG. 1. The wireless communication network 100 comprises a radio basestation, BS, 110, sometimes also in the art referred to as a node B, anda plurality of User Equipments, UEs, 120:1-6. Some of the UEs, 120:1-4are in active communication with the BS 110, which in the figure isindicated with solid arrows, while the other UEs 120:5-6 are in astandby mode, however still maintaining some control signaling with theBS 110 (dashed arrows). The BS 110 and at least some of the UEs, UEs120:3-5, are configured to communicated over a plurality of links, forexample multi-antenna arrangements adapted for MIMO-based communication.The channel characterization relies on pilot signaling on the commonpilot channels, the CPICH channels. Each transmit antenna, or antennastream is associated with one CPICH.

The term “radio base station” should be given a broad interpretation,including the meaning of a BS as it is conceived in current wirelesssystems such as GSM and UMTS, but also a radio node that does not haveto be fixed, and/or only occasionally has the role of a BS, in forexample an Ad-hoc network.

The UEs may for example be a mobile phone, a user equipment of variouskinds: such as laptop computers, PDAs, cameras, video/audio players andgame pads provided with radio communication abilities, a vehicle or astationary machine provided with radio communication abilities.

According to the method of the invention, a set of pilot sequences hasbeen defined, each pilot sequence comprising a pre-determined number ofsymbols. In a pilot signaling procedure in the BS 110 each pilot channelis assigned a specific pilot sequence from the set of pilot sequences.By letting a certain assignment of pilot sequences to the pilot channelsrepresenting a specific information, signaling information is conveyedto the UEs. It can be seen as a specific pilot sequence assignmentpattern corresponding to a specific information representation. The UEs120, having knowledge of the set of pilot sequences and the informationrepresented by different assignment patterns, can derive the signalinginformation by identifying which pilot sequences that were transmitted.The nature of this signaling, conveyed on pilot channels, makes it bestsuitable for broadcast-type control signaling. The pilot sequences andthe information represented by the pilot sequence assignment patterns ispreferably standardized.

The principle of the invention is schematically outlined in FIG. 2. InFIG. 2, three antennas C₁, C₂ and C₃ and a set of separate pilot signalsor sequences, {P₁, P₂, . . . P₆}, for example, are available. At a firsttime instance, T₁, pilot sequence P₁ is transmitted from antenna C₁, P₃from C₂, and P₅ from C₃, representing first information, illustratedwith “A”. At a second time instance T₂, P₂ is transmitted from antennaC₁, P₄ from C₂, and P₆ from C₃, representing second information,illustrated with “B”.

The method according to the invention, suitable for the communicationsystem outlined in FIG. 2, will be described with reference to theflowchart of FIG. 3, and comprises the steps of:

-   305: An update of broadcast-type parameters is initiated or    recognized by the BS 110. The BS determines control information to    be broadcasted, for example a parameter value or values.-   310: The BS 110 selects a pilot sequence assignment pattern, based    on a pre-determined relation between sequence assignment patterns    and control information. The pre-determined relation may for example    be in a form of a concordance list, shared between all nodes in the    system, relating pilot sequence assignment patterns to specific    information, parameter values etc.-   315: The BS 110 transmitting pilot sequences on the CPICHs according    to the selected pilot sequence assignment pattern.-   320: A UE 120 receives the pilots and determines the pilot sequence    assignment pattern by detecting which pilot sequence was used on    which CPICH.-   325: The UE 120 extracts the control signaling by using the    pre-determined relation between sequence assignment patterns and    control information. For example, the type of control information    and an associated parameter value can be derived by comparing the    determined pilot sequence assignment pattern with the pre-determined    concordance list.

A preferred embodiment of the invention is applicable to MIMO-basedsystems using more than two antennas. For a MIMO system to achievesignificant gains over a SIMO system, often 4 transmit antennas areneeded. According to this embodiment control information is signaled inthe CPICH channels from transmit antennas 3 and 4. A set of pilotsequences, S={s₁, s₂, s₃ . . . } is determined to be used in the system.Following the same CPICH spreading factor and transmission timeinterval, TTI, length as in Rel. 5, there are 30 pilot symbols per TTI.Pilot sequences can be chosen in a number of ways. A suitable choice isto use shortened Hadamard sequences. An example of length-32 Hadamardsequences is illustrated in FIG. 4a . These sequences may be shortenedin a simple way by taking the first 30 bits of each sequence, giving aset of (shortened) pilot sequences S′={s′₁, s′₂, s′₃, . . . , s′₃₀} asillustrated in FIG. 4b . According to the embodiment the pilot patternsof CPICH on 3rd and 4th antennas are determined based on 4 downlinksignaling bits. These downlink signaling bits can for example be used tosignal instantaneous power and code allocation to the UEs. Since thisinformation is updated in everyTTI, the SINR scaling error can beminimized, which will be discussed below. An example of how pilotpatterns are determined is shown in Table 1.

TABLE 1 Pilot patterns on 3rd and 4th antennas. CPICH on CPICH on x₄ x₃x₂ x₁ antenna 3 antenna 4 0 0 0 0 s′₁  s′₂  0 0 0 1 s′₃  s′₄  0 0 1 0s′₅  s′₆  0 0 1 1 s′₇  s′₈  0 1 0 0 s′₉  s′₁₀ 0 1 0 1 s′₁₁ s′₁₂ 0 1 1 0s′₁₃ s′₁₄ 0 1 1 1 s′₁₅ s′₁₆ 1 0 0 0 s′₁₇ s′₁₈ 1 0 0 1 s′₁₉ s′₂₀ 1 0 1 0s′₂₁ s′₂₂ 1 0 1 1 s′₂₃ s′₂₄ 1 1 0 0 s′₂₅ s′₂₆ 1 1 0 1 s′₂₇ s′₂₈ 1 1 1 0s′₂₉ s′₃₀ 1 1 1 1 s′₃₁ s′₃₂

Here x₁, x₂, x₃ and x₄ are the four downlink signaling bits. In theexample of signal power and code allocation, the four signaling bits canbe used to signal 16 quantized combinations of instantaneous power andcode allocation. Alternatively, they can be used to signal 16 quantizedinstantaneous power allocation in one TTI, and 16 quantizedinstantaneous code allocation in the next TTI. Alternatively, the foursignaling bits can be used to signal only the instantaneous codeallocation in every TTI.

In order to extract the signaling information bits, the UE needs tocorrelate with all possible pilot sequences in the set of pilotsequences to determine which pilot sequence is the most likely one usedon antennas 3 and 4. Such correlations are known in the art and fairlysimple operations and thus do not give rise to much complexity overhead.Further, the power allocated to CPICHs is strong enough for the UE toestimate channel coefficients. Such CPICH power will be sufficient forthe UE to make a reliable decision first regarding which pilot sequenceis used, because in making such a decision the UE enjoys a very largeprocessing gain (7680). Thus, x₁, x₂, x₃ and x₄ can be detectedreliably. After determining which pilot pattern is used, the UE mayperform channel and CQI estimation in the same way as any of theconventional methods. According to the method of the invention, there isno increase in code and power overhead associated to the signaling ofthese additional downlink signaling bits.

As appreciated by the skilled in the art, the above scheme can beextended to encompass more than four signaling bits, by using a largerset of pilot sequences. However, some practical limitations are given bythe number of possible pilot sequences for a given TTI length.

Other types of signaling information than the above exemplified may byconveyed in the pilot signaling according to the invention. Thebroadcast nature of the signaling information provided by the inventionmakes it best suited for broadcast or multicast control information. Thecontrol information may be updated every TTI, without increasing theload in the system, making the invention particular suitable for fairlyrapidly changing broadcast-type information. Such signaling informationinclude, but is not limited to the above mentioned signal power and codeallocation and parameters needed for network controlled feedback, SeeU.S. Patent Application 20060079221 “Network Controlled Feedback forMIMO Systems”. For network controlled feedback, a parameter named“feedback threshold” is broadcast by the base station to control theamount of feedback traffic in the uplink. The feedback threshold can bea SINR value. In this case, only user equipment which have received SINRhigher than the SINR threshold are allowed to feed back detailed channelquality information. Alternatively, the feedback threshold can be ascheduling metric. In this case, only user equipment which havescheduling metrics higher than the feedback threshold are allowed tofeed back detailed channel quality information. According to the presentinvention, this feedback threshold may by conveyed in the pilot symbolpatterns assigned to transmit antennas 3 and 4.

The invention has so far, for the reason of clarity only, been describedin a downlink scenario. As appreciated by the skilled in the art asimilar approach can be utilized also in uplink. The method can be usedalso in Ad hoc networks wherein a UE temporarily acts as a base stationand distribute pilot signals.

Arrangements according to the present invention in a radio base stationand user equipment, respectively, suitable for effectuating the abovedescribed embodiments are schematically illustrated in FIGS. 5a and 5b .The modules and blocks according to the present invention are to beregarded as functional parts of a base station and/or a user equipmentin a communication system, and not necessarily as physical objects bythemselves. The modules and blocks are preferably at least partlyimplemented as software code means, to be adapted to effectuate themethod according to the invention. However, depending on the chosenimplementation, certain modules may be realized as physicallydistinctive objects in a receiving or sending node. The term“comprising” does primarily refer to a logical structure and the term“connected” should here be interpreted as links between functional partsand not necessarily physical connections. As is well known in the art, aspecific function can be made to reside in different nodes in thecommunication system, depending on the current implementation. Thus, themeans in the following ascribed to a sending/receiving node (basestation or a user equipment), could at least partly be implemented inanother node in the system, for examples in a radio network controller(RNC), but made to effectuate the signalling from the sending/receivingnode.

The base station 505 comprises radio communication means 510, whichprovides the necessary functionalities for performing the actualreception and transmission of radio signals and is well known by theskilled person. The base station is typically a part of an accessnetwork. The radio communication means 510 are adapted for communicationvia a plurality of antennas 515. An antenna stream and one CPICH areassociated to each antenna. The radio communication means 510 isconnected to control signal processing means 520 adapted to handlecontrol signalling with other radio nodes. According to the inventionthe radio communication means 510 and the control signal processingmeans 520 of the base station 505 are adapted to effectuate transmissionof different pilot sequences on different antennas. The control signalprocessing means 520 is connected to a pilot sequences storage 525storing the pilot sequences relevant for the communication system. Thecontrol signal processing means 520 is further connected to a pilotsequences pattern storage 530 comprising a list of the pre-determinedrelation between specific pilot sequences patterns and specific controlinformation. The base station may further comprise analysing anddetermining means 535, in connection with the radio communication means510 and the control signal processing means 520, adapted to, forexample, collect and analyse data on signal quality and to determinesuitable code and power allocation. A requirement for control signallingmay be recognized by the analysing and determining means 535, orcommunicated to the base station from other parts of the access network.Upon such request the control signal processing means 520 determines thepilot sequences pattern, or patterns, by retrieving the relation betweenthe control information and the pilot sequences pattern from the pilotsequences pattern storage 530. The individual pilot sequences areretrieved from the sequences storage 525 by the control signalprocessing means 520. The control signal processing means 520 has thusdetermined a set of pilot sequences and instructs the radiocommunication means 510 to transmit the set.

The user equipment 555 comprises radio communication means 560, whichprovides the necessary functionalities for performing the actualreception and transmission of radio signals and is well known by theskilled person. The user equipment is preferably provided with aplurality of antennas 565 and the radio communication means are capableof discerning signals simultaneously transmitted on different channels,for example different pilot sequences. Control signal reception means570 is adapted to handle the control signalling of the user equipment.According to the invention the user equipment 555 is provided with apilot sequences storage 575, in connection with control signalprocessing means 570, and arranged to store the pilot sequences used inthe communication system. The control signal processing means 570 isfurther connected to a pilot sequences pattern storage 580 comprisingthe list relating specific pilot sequences patterns with specificcontrol information. The control signal processing means 570 is adaptedto use information retrieved from the pilot sequences pattern storage580 to interpreted the meaning of a received pilot sequences pattern.The thus received and interpreted control information may for example beused by the control signal processing means 570 to instruct the radiocommunication means 560 to adjust transmission parameters in furthercommunication.

The user equipment may for example be a mobile station, a laptopcomputer, a PDA, a camera, a video/audio player or a game pad providedwith radio communication abilities. Other examples include, but is notlimited to machinery provided with radio communication abilities, suchas vehicles or stationary machines such as automatic vending machines.

An implementation of the invention will be described with reference toPARC-MIMO used for HS-DSCH as a non-limiting example. In PARC-MIMO it isof high importance for maintaining a high CQI estimation accuracy, thatthe BS 210 can broadcast updates of power and/or code allocationinformation to the UEs. The information facilitates accurate SINRestimates in the UEs. As indicated in the background PARC-MIMO requiresfeedback of the per-antenna rates which are based on thesignal-to-interference-plus-noise ratios (SINRs) at each stage of theSIC.

SINR feedbacks are already needed for the rate adaptation processemployed for HS-DSCH to enhance the spectral efficiency. With rateadaptation, the Node B selects an appropriate data transmission ratesuitable for a given channel condition. Thus, when the channel is in adeep fade, a lower data transmission rate is used, whereas when thechannel condition is good, a higher data transmission rate is used. Rateadaptation can also be used to account for the variation of code andpower availability. When the Node B has lots of available codes andavailable power, a higher data transmission rate is used. On the otherhand, when the Node B has only very limited amount of unused codes andpower, a lower data transmission rate is used. The adaptation process isillustrated in FIG. 6. To facilitate rate adaptation, all the standbyUEs have to report back, step 615 to the Node B a channel qualityindicator (CQI), which is typically a quantized version of the RAKEreceiver SINR, measured, for example, at the output of SIC-GRAKEreceiver. The SINR can be the symbol SINR on a single code of theHS-DSCH, or can be the aggregate SINR on all the codes of HS-DSCH. Notethat the aggregate SINR on all the codes is simply the symbol SINR on asingle code times the number of codes allocated to the HS-DSCH. For thepurpose of this description CQI will be equated to the symbol SINR atthe output of SIC-GRAKE. In the rate adaptation process, a UE, withoutthe knowledge of instantaneous code and power available at the servingNode B, typically estimates in step 610 the output symbol SINR accordingto a nominal code and power allocation. In SISO operations, nominal codeallocations are defined in CQI tables, standardized by the 3GPP, usedfor rate adaptation, where the nominal power allocation is signaled inone of the downlink control channels, step 605. Note that these nominalcode and power allocations are established for the purpose of CQImeasurement and reporting, and are not intended for reflecting theactual code and power availability at Node B. In fact, the controlchannel that carries the nominal power allocation has a very slow updaterate.

After receiving the CQI feedback, the Node B would need to scale thereported SINR according to the instantaneous code and power that will beallocated to the UE, step 620. This adjusted SINR is then used to selectan appropriate modulation and coding scheme (MCS) in step 625.

In a MIMO based system, scaling process performed in Node B is undercertain circumstances non-trivial. In general, the output symbol SINR indB can be modeled approximately as a linear function of code and powerallocation. However, the linear scaling slope depends on I_(or)/I_(oc),multipath delay profile, as well as the code and power allocation. Here,I_(or) is the total power received from the serving Node B, and I_(oc)is the total power received from all the other base stations plusthermal noise. SINR scaling at the Node B, if not done correctly, willresult in the adjusted SINR to be very different from the true SINR. Ifthe adjusted SINR is too high, the selected transmission data rate ishigher than the rate that the radio channel can support. This oftenresults in errors in the transmitted data. If the adjusted SINR is toolow, the selected transmission data rate is lower than the rate that theradio channel can support. In either case, the system throughput isdegraded.

The G-RAKE output symbol SINR can be described as:

$\begin{matrix}{{SINR} = {\frac{\alpha}{K}h^{H}R^{- 1}h}} & (1)\end{matrix}$

where α and K are the total power and number of spreading codesallocated to the HS-DSCH, respectively, and h and R are net response andimpairment covariance matrix, respectively. The ratio α/K can beinterpreted as the power allocated to each of the HS-DSCH codes. In SISOSystems, the noise covariance matrix R can be measured directly from theCPICH. It can be shown that in the SISO case, R is independent of powerallocation on the downlink code channels. As a result, SINR in dB scaleslinearly, with slope 1 or −1 with respect to power allocation (α) andcode allocation (K), respectively.

For rate adaptation in a SISO System, the UE estimates an SINR based onreference power and code allocations α_(ref) and K_(ref), respectively.The factors α_(ref) and K_(ref) are established as a common referencefor the purpose of SINR estimation, and are typically not the same asthe actual instantaneous power and code allocations, denoted by α_(inst)and K_(inst), respectively. In this setup, the SINR estimated in the UEis therefore

$\begin{matrix}{{SINR}_{ref} = {\frac{\alpha_{ref}}{K_{ref}}h^{H}R^{- 1}h}} & (2)\end{matrix}$

The estimated SINR will then be reported back to the Node B through CQIfeedbacks. and the Node B will need to scale SINR_(ref) for theinstantaneous power and code allocations. Note that the instantaneousSINR is

$\begin{matrix}{{SINR}_{inst} = {{\frac{\alpha_{inst}}{K_{inst}}h^{H}R^{- 1}h} = {\frac{\alpha_{inst}}{\alpha_{ref}}\left( \frac{K_{inst}}{K_{ref}} \right)^{- 1}{SINR}_{ref}}}} & (3)\end{matrix}$

Converting eq. (3) to dB yields:

$\begin{matrix}{\left( {SINR}_{inst} \right)_{d\; B} = {\left( \frac{\alpha_{inst}}{\alpha_{ref}} \right)_{d\; B} - \left( \frac{K_{inst}}{K_{ref}} \right)_{d\; B} + \left( {SINR}_{ref} \right)_{d\; B}}} & (4)\end{matrix}$

Thus. the instantaneous SINR in dB scales linearly with both power andcode adjustments. and with scaling slopes 1 and −1, respectively.

In the PARC case, the SIC-GRAKE Output SINR for the m:th stream can beshown as

$\begin{matrix}{{{SINR}(m)} = {\frac{\alpha (m)}{K}{h^{H}(m)}{R^{- 1}(m)}{h(m)}}} & (5)\end{matrix}$

where α(m) is the power allocated to MIMO channels on antenna (or datastream) m, K is the number of MIMO channelization codes, and h(m) andR(m) are respectively, the net response and noise covariance for them:th stream. The noise covariance for the m:th decoded stream can beexpressed as [3]

R(m)=R _(cpich) +R _(CR)(m)−R _(SIC)(m)  (6)

where R_(cpich) is the noise covariance measured from the CPICH, R_(cr)is contributed by code-reuse interference, and R_(sic)(m) accounts forthe interference removed during the SIC process prior to the m:thdecoding stage. The code-reuse term R_(cr) is given as

$\begin{matrix}{{R_{CR}(m)} = {\frac{\alpha}{K}{\sum\limits_{n = {m + 1}}^{M}{{h(n)}{h^{H}(n)}}}}} & (7)\end{matrix}$

Wherein it is assumed that the MIMO power is evenly distributed acrossactive transmit antennas, α(1)=α(2)==α(M)=α, where Mα is the total basestation power allocated to the MIMO user of interest, and α/K is thepower per MIMO code, per active transmit antenna. It should be notedthat R_(cr) depends on power and code allocations. Furthermore, the termR_(sic)(m) also depends on MIMO power allocation α because SIC isapplied to own MIMO signals only. These two factors impact the SINRscaling issue significantly because in this case SINR(m) depends on Kand α in a more convoluted manner,

$\begin{matrix}{{{SINR}(m)} = {\frac{\alpha}{K}{h^{H}(m)}{R^{- 1}\left( {m,\alpha,K} \right)}{h(m)}}} & (8)\end{matrix}$

In this case, SINR scaling is much more complicated than what equation(3) indicates. Thus, for the PARC case, it is beneficial to signal thecode and power availability to the user equipment. This way there is noneed to further scale the reported CQI. Or, the error introduced in theSINR scaling step can be minimized if there is a change in instantaneouscode and power availability since the last time such information isprovided. Using the method of the invention, code and power allocationcan be signaled by selecting the pilot symbol patterns to be transmittedby antennas 3 and 4. For example, using a scheme as described in Table1, 4 bits of control information can be signaled. The base station canuse these 4 bits to signal 16 different code allocations, or 16different power allocations, and 16 different combinations of code andpower allocation.

The method and arrangement according to the invention have beendescribed primarily with reference to MIMO-based systems. It should benoted that the method and arrangement equally well may be utilized alsoin other communication systems utilizing a plurality of radio paths forthe communication between radio nodes, for example cooperative relayingsystem.

The method and arrangement according to the invention have beendescribed primarily with reference to a CDMA system. It should be notedthat the method and arrangement equally well may be utilized also insystems utilizing other access technologies such as Orthogonal FrequencyDivision Multiplexing (OFDM).

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, on the contrary, is intended to cover variousmodifications and equivalent arrangements as defined by the appendedclaims.

1-27. (canceled)
 28. A method for use in a user equipment of controlsignaling in a wireless communication network, wherein the userequipment transfers control information to at least one radio basestation, and wherein a plurality of common pilot channels are availablebetween the user equipment and the radio base station, wherein animprovement comprises: defining a set of unique pilot sequences; andassigning, by the user equipment, specific pilot sequences from the setof pilot sequences to specific common pilot channels, thereby forming apilot sequence assignment pattern that represents specific controlsignaling information.
 29. The method according to claim 28, wherein theassigning step includes the user equipment using a list ofpre-determined relations between pilot sequence assignment patterns andcontrol information to determine the pilot sequence assignment pattern;wherein the radio base station uses a corresponding list of relationsbetween pilot sequence assignment patterns and control information toextract the control information transmitted from the user equipment. 30.The method according to claim 29, wherein the pre-determined relation isformed as a concordance list, shared between all radio base stations anduser equipments in the network, relating pilot sequence assignmentpatterns to specific control information.
 31. The method according toclaim 28, wherein the specific control information comprises arepresentation indicating control information type and at least oneparameter value.
 32. The method according to claim 28, wherein twocommon pilot channels are used for the control signaling.
 33. The methodaccording to claim 28, wherein the control signaling information conveysinformation about a current power or code allocation of the radio basestation.
 34. The method according to claim 28, wherein the communicationnetwork is a Multiple-Input-Multiple-Output (MIMO)-based network, andthe plurality of common pilot channels relates to the plurality oftransmit antennas provided by a MIMO configuration.
 35. A method for usein a radio base station of control signaling in a wireless communicationnetwork, wherein the radio base station receives control informationfrom a user equipment, and wherein a plurality of common pilot channelsare available between the radio base station and the user equipment,wherein an improvement comprises: defining a set of unique pilotsequences; and receiving, by the radio base station, specific pilotsequences from the set of pilot sequences transmitted by the userequipment on specific common pilot channels, thereby forming a pilotsequence assignment pattern that represents specific control signalinginformation.
 36. The method according to claim 35, further comprisingthe radio base station using a list of pre-determined relations betweenpilot sequence assignment patterns and control information to determinethe pilot sequence assignment pattern; wherein the user equipment uses acorresponding list of relations between pilot sequence assignmentpatterns and control information to assign the specific pilot sequencesfrom the set of pilot sequences to the specific common pilot channels.37. A radio base station for control signaling in a wirelesscommunication network, wherein the radio base station is configured toreceive control information from a user equipment, and wherein aplurality of common pilot channels are available between the radio basestation and the user equipment, wherein an improvement comprises: amemory for storing a defined set of unique pilot sequences; a receivingcircuit configured to receive specific pilot sequences from the definedset of pilot sequences transmitted by the user equipment on specificcommon pilot channels, thereby forming a pilot sequence assignmentpattern that represents specific control signaling information; and aprocessing circuit configured to utilize a list of relations betweenpilot sequence assignment patterns and control information to extractthe control information transmitted from the user equipment.
 38. Theradio base station according to claim 37, wherein the list of relationsis stored in a pilot sequences pattern storage in a form of aconcordance list, shared between all radio base stations and userequipments in the network.
 39. The radio base station according to claim37, wherein the control information comprises a representationindicating control information type and at least one parameter value.40. The radio base station according to claim 37, further configured touse two common pilot channels for the control signaling, providing fouruplink signaling bits.
 41. A user equipment for control signaling in awireless communication network, wherein the user equipment is configuredto transfers control information to at least one radio base station, andwherein a plurality of common pilot channels are available between theuser equipment and the radio base station, wherein an improvementcomprises: a memory for storing a defined set of unique pilot sequences;a processing circuit configured to assign specific pilot sequences fromthe set of pilot sequences to specific common pilot channels, therebyforming a pilot sequence assignment pattern representing specificcontrol signaling information; and a transmitting circuit configured totransmit the assigned specific pilot sequences on the specific commonpilot channels.
 42. The user equipment according to claim 41, wherein apre-determined relation is stored in a pilot sequences pattern storagein a form of a concordance list, shared between all radio base stationsand user equipments in the network.
 43. The user equipment according toclaim 41, wherein the control information comprises a representationindicating control information type and at least one parameter value.44. The user equipment according to claim 41, wherein the user equipmentis configured to use two common pilot channels for the controlsignaling, providing four uplink signaling bits.